1. Field of the Invention
The present invention relates to a pneumatic tire provided in the tread portion with sipes, more particularly to an improved shape of a sipe being capable of preventing the siping blade of a tire vulcanizing mold from bending and coming off therefrom at the time of removing the vulcanized tire from the mold.
2. Description of the Related Art
In general, pneumatic tires such as snow tire and studless tire called winter tire are provided in the tread portion with a number of sipes to improve on-the-ice performance. Such performance may be improved by increasing the number of the sipes and/or the length of the sipes.
In recent years, on the other hand, in order to engage the side walls of a sipe with each other and thereby to give support to each other, the use of a sipe having three-dimensional side walls has been proposed.
In case of a sipe having three-dimensional side walls, however, when the vulcanized tire is removed from a tire mold, as the resistance becomes increased, there is a tendency for the siping blades to be deformed and come off from the mold. From a practical standpoint, therefore, it is difficult to increase the number and length of the sipes.